General windpower
information

When seen in the wider landscape it is often difficult to judge the size of a turbine without something to scale it against.

The diagram below shows scale representations of the most popular wind turbines that we specify, alongside Big Ben to give you an idea of their scale. The table below then summarises each turbine’s specifications. Note – the 100 kW turbine is the smallest scale that we develop.

Wind Turbine Scales

Some sites are windier than others. A lowland site in the middle of southern England might have an average wind speed of 6 m/s, whereas an exposed site on the top of a hill on the west coast of Wales or Scotland might have an average wind speed of 9 m/s.

Because the ‘power in the wind’ is proportional to the cube of the velocity, this means that the wind turbine on the 9 m/s site would on average be exposed to well over three-times the loads compared to the 6 m/s site. Clearly this means that the more exposed wind turbine will have a tougher life and will be subjected to greater wear and tear.

To avoid having to make over-engineered wind turbines that could all operate reliably on all sites, no matter how windy they were, manufacturers design their wind turbines for a specific Wind Class.  A Wind Class 3 turbine is designed for an easy life with average wind speeds up to 7.5 m/s, and these turbines typically have extra-large rotors to allow them to capture as much energy as possible from the lower wind speeds they are subjected to.

Wind Class 2 turbines are for windier sites up to 8.5 m/s average, and are the most common class of wind turbines available.

Wind Class 1 turbines are designed to cope with the tough operating conditions experienced at sites with average wind speeds above 8.5 m/s. Typically these turbines have smaller rotors (i.e. shorter blades) and are on shorter towers to minimise structural loads. They are also heavier-duty in design, which makes them more expensive.

There is also a second dimension to each wind class which is ‘turbulence intensity’, which is basically a measure of how turbulent the wind is at a site. This is important because complex topography can cause turbulence, and turbulence can cause varying loads on wind turbines which causes them to wear more quickly. In extreme cases, if a site is just too turbulent the wind turbine manufacturer will refuse to supply a wind turbine because they will know that the turbine will not operate reliably for the full design life at such a site.

Basically, for wind class 2 and wind class 1 sites onsite wind monitoring is essential to determine the exact annual average wind speed and the turbulence intensity, so that the optimum turbine can be specified to ensure long term, reliable operation. Class 3 sites can sometimes get away without having to do wind monitoring because the wind turbine manufacturer will be confident that the loads on the turbine will be acceptable (though site owners often still want wind monitoring so they can be sure of the income the wind turbine will generate).

The table here shows the IEC Wind Classes and the wind speeds that the turbine must be designed to withstand.

Yes, you can consume energy onsite, provided that the wind turbine can connect into the site distribution board. Sometimes this is not possible because the wind turbine site is geographically separate from the site distribution board, or the cable run would be excessively long.

Whenever possible the preferred option would be to connect into the site distribution board because this allows you to offset imported energy which significantly increases the income from the wind turbine.

It is important to remember that electricity flows like water and will always follow the easiest route to the nearest load; this means that all of the site owner’s loads (i.e. lighting, sockets, machinery, air conditioners etc.) that connect to the same distribution board would be supplied firstly by the wind turbine, and only once all of these loads had been satisfied would any surplus energy from the wind turbine flow backwards through the incoming supply cables, either to the next nearest distribution board on the site, or out through the export meter to the grid.

Also, because the electricity produced by the wind turbine is fully grid-synchronised, it will mix seamlessly with grid-imported electricity. This means that if the wind turbine cannot supply all of the site’s loads, then all of the electricity from the wind turbine would go towards the loads and any deficit would be seamlessly imported from the grid.

Equally, if the wind turbine was supplying all of the local loads but then a reduction in the wind speed caused the output to suddenly drop, then the grid would instantly supply more to make up the deficit. From a consumers point of view, the source of the electricity would be unknown; it could be from the wind turbine, the grid or a combination of both.

In the situation where the on-site loads far exceed what the wind turbine could ever produce, then all of the electricity generated by the wind turbine would be consumed onsite. For example, if a wind turbine with a maximum power output of 500 kW was connected to a site that had a baseload (i.e. the minimum load 24/7) of 1 MW, then 100% of the energy generated by the wind turbine would be consumed on site.

If it is not physically possible to connect to the onsite distribution board or the generation system is significantly larger than the onsite loads, or there simply isn’t an on-site distribution board, then the system would be directly connected to the grid via a dedicated grid connection.

Possibly…

To be able to go ‘off-grid’ and supply yourself with electricity is very complicated because you have to balance the supply of electricity from the wind turbine, which varies with wind speed, with the loads on your site which also vary as things are turned on and off.

This can be achieved via some of the large-scale battery storage systems that are becoming available, but even then, tends to be to cover short-duration power cuts of up to about an hour, rather than for long-term off-grid operation. Battery storage at commercial-scale is still relatively expensive, but it does bring other benefits like the ability store energy for use later, or take advantage of the low and high electricity prices to buy and sell electricity into the wholesale market.

Long-term off-grid operation is possible, but the system is much more complicated from an electrical perspective and will generally need some form of ‘ultimate backup’ like a diesel generator. Unless you have no choice, we wouldn’t recommend this option.

Modern wind turbines are remarkably quiet. It is one of the odd things about the anti-wind lobby that they often focus on noise as an issue, when in reality anyone who has stood close to a modern wind turbine knows how little noise they make.

The rules that must be followed to obtain planning consent state that if the noise level after modelling at nearby neighbours is less than 35 dB(A) then no further work is required and all is OK. 35 dB(A) is approximately the noise level inside a quiet library or a quiet whisper.

If after noise modelling the noise level is predicted to be between 35 and 40 dB(A) then background noise measurements must be done to confirm just how quiet the area is (normally background noise levels are somewhere between 35 to 40 dB(A) in very quiet rural areas), and then the limit is set at the greater of 40 dB(A) or background + 5 dB(A).

If after modelling and background noise measurements the turbine noise level at a neighbouring property is more than 40 dB(A) or background + 5 dB(A), then that neighbour must be ‘financially involved’ in the project, which normally means the neighbour being paid some of the income generated by the wind turbine. Even at 45 dB(A) this is very, very quiet and most people would hardly ever notice.

If you want to know how quiet wind turbines are the best thing to do is to go and visit one. Many wind turbines are in accessible places and are perfectly safe to walk right up to and listen to. One you’ve stood right underneath, walk about 400 metres away (this is around the minimum separation from a neighbour that would be allowed) and see if you can still hear the wind turbine at all.

Obtaining planning consent and an acceptable grid offer are always the biggest project risks for wind power.

A good quality wind feasibility study will determine whether the site should technically get planning consent, but there is still the risk that you will get a planning officer and/or planning committee that are anti-wind. If required there is the planning appeal process, though this can be a lengthy and expensive route to take.

Obtaining grid connection for a reasonable cost is also a significant risk. If the electricity distribution grid is weak in your area then an expensive grid upgrade could be required before a wind turbine could be connected. It is important to get a grid offer early during the wind project, so that you know whether grid connection is possible and what any grid upgrades would cost.

Aviation (radar) objections from the MOD, CAA (Civil Aviation Authority) or NATS (National Air Traffic Services) can be show-stoppers. The best way to identify if there is a risk is to complete a full aviation study early in the project, and if any issues are highlighted engage with the relevant stakeholder and try to get a written resolution before proceeding with a planning application. If there is an objection due to radar interference, it is possible to sometimes overcome this by using an aviation radar specialist to model the likely interference and then argue with the case. The MOD in particular has been known to take an unreasonably tough stance against wind turbines, which with careful modelling and a strong case can be overturned.

Another problem can be a local ‘anti-wind’ group. Although the arguments promoted by anti-wind groups are now largely discredited, they can still slow down the whole planning process and make the atmosphere ‘tense’ between the landowner that wants a wind turbine and local members of the anti-wind group. Patience, determination and a thick skin are the best defence.

Yes, Renewable UK.

See their website here https://www.renewableuk.com. The website contains a wealth of information about wind turbines.

If you are interested in installing a wind turbine, the first step is to contact us to discuss your requirements and to complete a Wind Turbine Feasibility Study.